That solution is terrible, with a bad algorithm that requires O(tree_height) space (the optimal one involves temporarily using left/right pointers as a parent pointer so that you only need constant space) and lacking any sort of assembly optimization, being worse than what a compiler would produce (e.g. it's a real mystery how the author managed to decide that local_right should be spilled on the stack).

Definitely not what you want to submit to someone testing your programming skills.